Electronic tube apparatus



April 8, 1950 D. H. SLOAN 2,504,894

ELECTRONIC TUBE APPARATUS Filed Oct. 31, 1945 3 Sheets-Sheet lWITNESSES: INVENTOR D7577 BY April 1950 DLH. SLOAN 2,504,894

ELECTRONIC TUBE APPARATUS F1163 Oct. 31, 1945 3 Sheets-Sheet 2WITNESSES:

INVENTOR April 18, 1950 D. H. SLOAN 2,504,894

ELECTRONIC TUBE APPARATUS Filed Oct. 31, 1945 3 Sheets-Sheet 3 57 J197-7 E| I? 6 a5 fl :n /2

WITNESSES: INVENTOR 7 W. M flaw/db. 5/0427.

Patented Apr. 18, 1950 UNITED STATES PATENT OFFICE ELECTRONIC TUBEAPPARATUS Application October 31, 1945, Serial No. 625,910

18 Claims.

Thi invention relates to electronic tube apparatus and has particularrelation to high frequency apparatus involving a magnetron tube.

In a magnetron tube constructed in accordance with the teachings of theprior art, the anode may be mounted within an anode chamber, such as acopper cylinder which serves both as a resonant cavity and as a vacuumenvelope. Operation of the magnetron requires a substan tially uniformmagnetic field within the copper cylinder and substantially parallel tothe axis thereof. To obtain such a field, two arrangements are in commonuse. In one arrangement, an air core solenoid winding surrounds thecopper cylinder without important iron structures in the field. Theother arrangement includes an iron yoke with magnet coils wound thereon,the yoke being arranged to have pole pieces between which the coppercylinder is positioned.

To introduce the output of the prior magnetron into a hollow wave guide,a coaxial line coupling section is provided with the center conductorthereof extending into and forming a loop within the copper cylinder atone end and extending into and forming a loop within the wave guide atthe other end.

The apparatus described may be operated satisfactorily, being usuallyemployed in producing high frequency oscillations. However, the magneticcircuit arrangement is rather clumsy and interferes with the arrangementof other parts of the apparatus nearby. Moreover, the coaxial couplingsection requires various tuning and matching elements and is always asource of trouble. In addition, the coaxial coupling section tends todecrease the band width of the apparatus.

It is, accordingly, an object of my invention to provide a new andimproved magnetron apparatus.

Another object of my invention is to provide a new and improved magneticcircuit for use with an electronic tube, such as a magnetron.

A further object of my invention is to provide a new and improvedarrangement for coupling a magnetron to a load device.

Still another object of my invention is to provide a new arrangement forcoupling the output of a high frequency generator into a wave guide.

More specifically, it is an object of my invention to provide a novelmagnetron tube apparatus with an improved magnetic circuit arrangementand a more efiioient and less troublesome coupling of the magnetron tubeto the load.

winding surrounds the anode chamber of a magnetron tube. The winding hasan external shell of magnetic material cooperating with pole pieces ofmagnetic material built into the magnetron tube to effect asubstantially complete enclosure of magnetic material about the windingand anode chamber, with the pole pieces ar ranged to establish asubstantially uniform field within the chamber. With such anarrangement, a short high frequency lead of the resonant circuit of themagnetron is brought out of the anode chamber into the field free spacejust outside the enclosure of magnetic material to be coupled directlyinto the load equipment, such as a wave guide or a cavity resinator, asby an output coupling loop formed in said lead. Further improvement inthe coupling may be provided by means of vanes or dome-like structuresmounted on the output coupling loop to contribute capacitive coupling inproper phase to add to the magnetic coupling provided by the loop.

The novel features, which I consider cha teristic of my invention, areset forth with greater particularity in the accompanying claims. Theinvention itself, however, together with additional advantages andobjects thereof may be better understood from the following descriptionof specific embodiments when read in connection with the accompanyingdrawings in which:

Figure 1 is a cross-sectional view of apparatus including a magnetrontube of the split-anode type arranged to supply energy to a wave guide.

Fig. 2 is a partial end view of the apparatus taken along line 11-11 ofFig. 1.

Fig. 3 is a partial sectional view taken along theline III-III of Fig.1.

Fig. 4 is a cross-sectional view taken along the line IVIV of Fig. l,the view of Fig. 1 having been taken along the line I-I of Fig. 2, and

Figs. 5 and 6 are partial sectional views illustrating alternatecoupling arrangements.

A magnetron of the split-anode type is shown in the drawings andcomprises a generally cylindrical anode chamber ll comprising a pair ofend plates l3 and i5 and a connecting cylindrical wall it therebetween.A ring-like magnetic coil Iii surrounds the cylindrical wall I! of theanode chamber it. An external shell of magnetic material, such as ironor steel, is provided about the coil l9 and includes a pair of flatring-like plates 2! l on each end and another ring member 23 about thecircumference of the coil 19. The coil In accordance with my invention,a solenoid and shell are conveniently held together by means the anodechamber I'l. mounted on the cathode 25,- as shown in Fig. 4,

3 of supporting plates 22 at each end connected by bolts 24.

The two end plates i3 and I5 of the anode chamber H are also of magneticmaterial and cooperate with the external shell about the coil 19 toprovide a substantially complete enclosure of magnetic material aboutthe coil l9 and chamber ll. Consequently,-the end plates l3 and I5 serveas pole pieces and a magnetic field is established within the anodechamber between the two end plates which is substantially uniform andsubstantially parallel to the axis of the anode chamber.

Inasmuch as the end plates 13 and I5 of the anode chamber, which serveas pole pieces, are

of magnetic material, it is extremely" desirable from the standpoint ofmanufacturing of the tube to employ the same material for thecylindrical wall l1. However, it is necessary to avoid harmfuldistortion as a result of shunting the magnetic field within the anodechamber between the two end plates l3 and i5. I have found that:m'agnetic'material may be used forthe cylindrical wall I!interconnecting the two end plates if the wall is of such dimensionsthat it is saturated by the magnetic flux flowing 'therethrough.

-With such an arrangementthe usual magnetomotive'force remains effectiveacross the region between the end'plates l3 and i5 and harmfuldistortion of the field'is avoided.

A generally cylindrical cathode '25 of the secondary'emitter type ismounted-coaxially within A small filament '21 is to provide electronsfor initiating oscillations within the tube. The cathode 25 is supportedon a long hollow stem 29 which extends through an opening 3! in theupper end plate I5 of the anode chamber H, being secured to the endplate l5 by a tubular member 33'but insulated therefrom "stem 29 andwhich are to be cooled by the passage of cooling fluid through pipes 43.

Aspreviously indicated, the magnetron is of the split-anode type. Theanode includes a pair of anode members 45 and 41 of highly conductivematerial, such as copper, arranged to form a generally cylindricalstructure surrounding the cathode 25 as shown in Fig. 3, the innersurface of each anode member 45 and 41 approximating a semi-cylinder.Each ofthe anode members 45 and 41 is supported by a corresponding con--ductive post Hand" 5!", respectively, mounted on theupper end platel5'of the anode chamber H. The posts 49 and 5-! provide inductance forthe "resonant circuit of the magnetron and they are positionedsubstantially parallel to the axis of the anode: structure.

Apair of frequency leads in the form of tubes 53 and 55,'preferably ofcopper, extend from the anode members 45 and 41, respectively, throughopenings 51 and 59 in the lower end plate l3 of the anode chamber ll.Below the lower end plate l3; each of the tubes 53 and 55 forms a loopand is-securedto'the'center of the end plate l3. The ends of'the tubes-53 and 55' forming the 'loops, open into opposite ends of a passageilprovided within the lower end plate l3. The posts 49 and 5! on which theanode members 45 and 41 are mounted, are hollow and a passage 63connecting therewith is also provided through each of the anode members45 and 41 to the interior of the tubes 53 and 55, respectively. Suitablecooling fluid, such as water, may then be circulated from supply lines65 connected to posts '49 and 5! through the posts, the anode members 45and M, the tubes 53 and 55 and the end plate 13.

For purposes of convenience in manufacture, the anodemembers may be madeof two parts with the cooling fluid passage extending therebetween 'asillustrated. In some cases, it may also be desirable to have asupporting post and at least part of the corresponding anode memberported in an internally threaded rotatable sleeve 15. mounted on endplate l5. Rotation of the sleeve 15 causes the screw E3 to be moved upor down resultingin an up or down movement of the tuning ring 6'!parallel to the axis of the anode structure. A plurality ofspring-biased guide pins 16, shown in Fig. 3, are mounted radially onsaid tuning ring 6! with their outer ends ar- .ranged to engage thecylindrical wall ll of the anode chamber H to guide the tuning ringduring movement thereof. A guide post ll mounted .on..the.upper endplate It serves to guide the movement of the supporting ring H, and apair of bellows 79 about the pipes 69 and secured to the upper end plate!5 permits such movement without loss of the vacuum within the chamberas discussed hereinafter. The movement of the tuning ring is preferablyarranged so that in its extreme upper position, the ring is positionedabout the posts 49 and 5i and in its extreme lower position, itsurrounds the anode members 45 and 41.

The outer surfaces of the anode members 45 and 41 are preferablysubstantially uniform in a direction parallel to the axis of thestructure. With the posts 49 and 5| substantially parallel to the axis,the posts are preferably so positioned and theouter surfaces of theanode members have such a configuration, that a considerable portion,about two-thirds in the embodiment illustrated, of the surface of eachpost forms, in

effect, an extension of the outer surface of the corresponding anodemember. The opening in the tuningring 6'! then preferably has the samegeneral configuration as the combined outer surfaces of the anodemembers, as shown in Fig. 3,

1 and is arranged so that when the ring surrounds the anode members,which circuit in many cases is included as part of the magnetron itself.In 'theillustrate'd arrangement, the resonant circult is included withinthe tube and comprises the supporting posts 49 and 5!, the anode members45 and 41 and tubes 53 and 55. In this resonant circuit the inductanceprovided by posts 49 and 5| and the capacitance between the anodemembers are of primary importance.

Now when the tuning ring 61 is in its extreme upper position, asillustrated in Fig. 1, it is closely adjacent to and partially surroundseach of the inductive posts 49 and 5|. Consequently, the tuning ring 61tends to obstruct an electromagnetic field about each of the posts andso causes the inductance of the posts to be at a minimum. At the sametime, the tuning ring Bl is a maximum distance from the anode members 45and 41 so the capacitance at the anodes is at a minimum. As a result,the resonant circuit is tuned to resonance at a relatively highfrequency.

On the other hand, when the tuning ring 61 is in its extreme downwardposition, the anode capacity is greatly increased while the inductanceof the posts is also increased. As a result, the resonant circuit istuned to resonance at a relatively low frequency. Any desired tuningbetween these two limits may be obtained by adjustment of the tuningring 61 between these two positions. This tuning arrangement isdescribed in my copending application, Serial No. 625,909, filed October31, 1945.

As previously indicated, the upper end plate l5 of the anode chamber isarranged to permit a vacuum within the chamber. However, the tubes 53and 55 extend through openings 5'! and 59 in the lower end plate I3 sothat the anode chamber is not vacuum tight. For this reason, a dome 8!of material transparent to electromagnetic waves, prefer'ably glass, ismounted across the lower end plate l3 with its base sealed to a ring 83of a suitable alloy having substantially the same coefiicient ofexpansion as the dome material, which ring is secured to the edge of endplate l3 through concentric rings 95 and 81. The dome 8| surrounds theoutput coupling loops formed by tubes 53 and 55 and completes a vacuumtight space including the interiors of the dome and the anode chamber,though of course, electromagnetic waves may pass through the dome. Thisspace is to be evacuated by means of a vacuum pump, not shown, which isassociated therewith.

The magnet coil i9 is arranged to be cooled by air under pressurethrough supply lines 68, the air passing through passages 19 providedthroughout the coil and out a plurality of openings T2 in ring 85. Theopenings 12 are arranged about the circumference of the seal at the baseof the glass dome BI and serve to cool the seal.

The tuning ring 67 is adapted to be cooled by cooling fluid suppliedthrough the supporting pipes 69 and circulated through a passage 90 inthe tuning ring.

Because of the enclosure of magnetic material about the coil l9 and theanode chamber II, a

wave guide or other device constituting the load,

may be positioned closely adjacent to the anode chamber and directlycoupled with the resonant circuit. A hollow wave guide89 whichconstitutes the load in the illustrated arrangement is provided in theform of a rectangular pipe of conductive material and has anend securedto the supporting plate 22 for the coil E9. The glass dome SI and thecoupling loops of tubes 53 and 55 within the dome, project into theguide 89. This provides a magnetic coupling between the magnetron andthe guide which is free from intermediate lines or branch circuits. Bysuch coupling the frequency band over which the coupling is correct isgreatly increased and a complex adjustment is not required for properloading.

The coupling loops of tubes 53 and 55 are shown as connected to thelower end plate l3 in the center thereof. However, this centerconnection may be eliminated if desired and the two tubes connecteddirectly together. The center connection is belived to be preferablehowever to provide a convenient path for the circulation of coolingfluid and a desirable structural support. In addition, the grounding ofthe coupling loops at approximately the center between the connectionthereof to the two anode members tends to suppress the undesirablesymmetric mode of oscillation of the magnetron, that is, the mode inwhich both anode members are positive at the same time.

A sheet metal shield is connected across the outer ends of the couplingloops to reduce the inductance provided by these loops in the resonantcircuit. The upper edges of this shield have portions 93 thereofadjacent the openings 51 and 59 in the lower end plate l3 through whichthe tubes 53 and 55 extend. These edge portions 93 are positionedcrosswise of openings 5'! and 59 to aid in preventing electrons from theinterior of the anode chamber from escaping into the dome 8!. The ring8'! is preferably copper plated steel and extends just inside the alloyring 83 to which the base of the glass dome BI is sealed to preventoverheating of the seal by eddy currents in the alloy ring.

The output loops of tubes 53 and 55 are part of the main resonantcircuit of the magnetron and couple the magnetron to the magnetic fieldwithin the guide 89 which may have the familiar rectangularcross-section. If it is desired to increase the coupling to therectangular guide 89, two vanes 95 and 91 may be attached to the loopsas in Fig. 5. These vanes 95 and 9'! extend parallel to the wider walls99 of the guide with one vane relatively close to each wall 59. Thevanes then contribute a capacitive coupling to the electric field in theguide 89 in proper phase to add to the magnetic coupling provided by thecoupling loops of tubes 53 and 55. This increased coupling is obtainedwithout increasing the self-inductance of the output loops and soenables the magnetron to operate at higher frequencies. This arrangementprovides a more uniform coupling over the wave length spectrum of themagnetron because the magnetic coupling is tighter at lower frequenciesand the capacitive coupling is tighter at higher frequencies.

Another arrangement for increasing the direct coupling to the wave guideis shown in Fig. 6. Here a metal dome-like structure Nil is attached tothe output loops. The sides of the dome structure provide a capacitivecoupling with the walls of the guide 89 with the improvements asdescribed in connection with the capacitive coupling of Fig. 5. Inaddition, the dome structure effectively short circuits the space withinit so that the inductance of the output loops is further reduced. Thisprovides an additional improvement in uniformity of coupling over awider range.

Although I have shown and described a preferred embodiment of myinvention, I am aware that many modifications thereof may be made andthat it may be applied to other electronic tubes without departing fromthe spirit of the invention. I, therefore, do not intend to limit myinvention to the specific embodiment and application described herein.

I claim as my invention: 1. Electronic tube apparatus for supplying highfrequency oscillations to a load comprising a vacuum tight envelopeincluding a, chamber, a magnet coil immediately surrounding said chamberand having an external shell of magnetic material, said chamberincluding a pair of end plates of magnetic material cooperating withsaid shell to provide a substantially complete enclosure of magneticmaterial about said coil and chamber, whereby a field may be establishedwithin said chamber between said plates, and a resonant circuitpartially within said chamber and including an output coupling loopextending through one of said end plates for direct magnetic coupling tosaid load.

2. Electronic tube apparatus for supplying high frequency oscillationsto a hollow, conductive load member comprising a vacuum-tight envelopeiorming a chamber, a magnet coil immediately surrounding said chamberand having an external shell of magnetic material, said chamberincluding a pair of end plates of magnetic material connected with saidshell to provide a substantially complete enclosure of magnetic materialabout said coil and chamber, whereby a field may be produced within saidchamber between said plates, and a resonant circuit partially withinsaid chamber and including an output coupling loop extending through oneof said end plates, said envelope also including a dome of materialtransparent to electromagnetic waves sealed across said one end plateand surrounding said output loop, said dome being adapted to projectinto said hollow load member whereby said loop provides direct magneticcoupling between said circuit and load member.

3. Electronic tube apparatus for supplying high frequencyelectromagnetic oscillations to a hollow, conductive load membercomprising a vacuum tight envelope forming a cylinder-like chamber, amagnet coil coaxial with and immediately surrounding said chamber andhaving an external shell of magnetic material, said chamber including apair of end plates of magnetic material connected with said shell toprovide a substantially complete enclosure of magnetic material aboutthe coil and chamber whereby a substantially uniform magnetic field maybe established within said chamber between said end plates, and

a resonant circuit partially within said chamber and including an outputcoupling loop extending through one of said end plates, said envelopealso including a dome of material transparent to electromagnetic wavessealed across said one end plate, said dome being adapted to projectinto said load member whereby said loop provides a direct magneticcoupling between said circuit and load member.

4. Electronic tube apparatus for supplying high frequencyelectromagnetic oscillations to a hollow, conductive load membercomprising a vacuum tight envelope forming a cylinder-like chamber, amagnet coil coaxial with and immediately surrounding said chamber andhaving an external shell of magnetic material, said chamber including apair of end plates of magnetic material connected with said shell toprovide a substantially complete enclosure of magnetic material aboutthe coil and chamber, said chamber also including a generallycylindrical wall of magnetic material interconnecting said end platesand saturable by the magnetic fiux therethrough while said coil isenergized, whereby a substantially uniform magnetic field maybeestablished within said chamber between said end plates, and a resonantcircuit partially within said chamber and including an output couplingloop extending through one of said end plates, said envelope alsoincluding a dome of material transparent to electromagnetic waves sealedacross said one end plate, said dome being adapted to project into saidload member whereby said loop provides a direct magnetic couplingbetween said circuit and load member.

5. Electronic tube apparatus for supplying high frequencyelectromagnetic oscillations to a hollow, conductive load member,comprising a vacuum-tight envelope including a chamber, a mag net coilimmediately surrounding said chamber and having an external shell ofmagnetic material, said chamber including a pair of end plates ofmagnetic material cooperating with said shell to provide a substantiallycomplete enclosure of magnetic material about said coil and chamber,whereby a field may be established within said chamber between saidplates, a resonant circuit partially within said chamber and includingan output coupling loop extending through one of said end plates andadapted to project into said load member to provide an inductivecoupling of the resonant circuit to the magnetic field within said loadmember, and a pair of conductive vanes attached to said loopsubstantially perpendicular to the plane of the loop and arranged toprovide a capacitive coupling to the electric field within said loadmember in additive phase with the inductive coupling of said loop.

6. Electronic tube apparatus for supplying high frequencyelectromagnetic oscillations to a hollow, conductive load member,comprising a vacuum-tight envelope including a chamber, a magnet coilimmediately surrounding said chamber and having an external shell ofmagnetic material, said chamber including a pair of end plates ofmagnetic material cooperating with said shell to provide a,substantially complete enclosure of magnetic material about said coiland chamber, whereby a field may be established within said chamberbetween said plates, a resonant circuit partially within said chamberand including an output coupling loop extending through one of said endplates and adapted to project into said load member to provide aninductive coupling of the resonant circuit to the magnetic field withinsaid load member, and a conductive dome-like structure attached to andsurrounding said loop to provide a capacitive coupling to the electricfield within said load member in additive phase with the inductivecoupling of said loop.

7. Electronic tube apparatus for supplying high frequencyelectromagnetic oscillations to a hollow, conductive load member,comprising a vacuum-tight envelope including a chamber, a magnet coilimmediately surrounding said chamber and having an external shell ofmagnetic material, said chamber including a pair of end plates ofmagnetic material cooperating with said shell to provide a substantiallycomplete enclosure of magnetic material about said coil and chamber,whereby a field may be established within said chamber between saidplates, a resonant circuit partially within said chamber and includingan output coupling loop extending through one of said end plates, saidenvelope also including a dome of material transparent toelectro-magnetic waves sealed across said one end plate and surroundingsaid loop and adapted to project into said load member whereby the loopprovides an inductance coupling of the resonant circuit to the magneticfield within said load member, and a pair of conductive vanes attachedto said loop within said dome substantially perpendicular to the planeof the loop and arranged to provide a capacitive coupling to theelectric field Within said load member in additive phase with theinductive coupling of said loop.

8. Electronic tube apparatus for supplying high frequencyelectromagnetic oscillations to a hollow, conductive load member,comprising a vacuum-tight envelope including a chamber, a magnet coilimmediately surrounding said chamber and having an external shell ofmagnetic material, said chamber including a pair of end plates ofmagnetic material cooperating with said shell to provide a substantiallycomplete enclosure of magnetic material about said coil and chamber,whereby a field may be established within said chamber between saidplates, a resonant circuit partially within said chamber and includingan output coupling loop extending through one of said end plates, saidenvelope also including a dome of material transparent toelectromagnetic waves sealed across said one end plate and surroundingsaid loop and adapted to project into said load member whereby the loopprovides an inductive coupling of the resonant circuit to the magneticfield within said load member, and a conductive dome-like structureattached to and surrounding said loop within said dome to provide acapacitive coupling to the electric field within said load member inadditive phase with the inductive coupling of said loop.

9. In combination, a hollow, conductive load member, a vacuum-tightenvelope forming a chamber, a magnet coil immediately surrounding saidchamber and having an external shell of magnetic material, said chamberincluding a pair 4 of end plates of magnetic material connected withsaid shell to provide a substantially complete enclosure of magneticmaterial about said coil and chamber, whereby a field may be producedwithin said chamber between said plates, and a resonant circuitpartially within said chamber and including an output coupling loopextending through one of said end plates, said envelope also including adome of material transparent to electromagnetic waves sealed across saidone end plate and surrounding said output loop, said dome projectinginto said hollow load member whereby said loop provides direct magneticcoupling between said circuit and load member,

10. In combination, a hollow, conductive load member. a vacuum-tightenvelope forming a cylinder-like chamber, a magnet coil coaxial with andimmediately surrounding said chamber and having an external shell ofmagnetic material, said chamber including a pair of end plates ofmagnetic material connected with said shell to provide a substantiallycomplete enclosure of magnetic material about the coil and chamberwhereby a substantially uniform magnet c field may be established withinsaid chamber between said end plates, and a resonant circuit partiallywithin said chamber and including an output coupling loop extendingthrough one of said end plates, said enevelope also including a dome ofmaterial transparent to electromagnetic waves sealed across said one endplate, said dome projecting into said load member whereby said loopprovides a direct magnetic coupling between said circuit and loadmember.

5 having an external shell of magnetic material,

said chamber including a pair of end plates of magnetic materialconnected with said shell to provide a substantially complete enclosureof magnetic material about the coil and chamber,

said chamber also including a generally cylindrical wall of magneticmaterial interconnecting said end plates and saturable by the magneticflux therethrough while said coil is energized, whereby a substantialyuniform magnetic field may be establishing within said chamber betweensaid end plates, and a resonant circuit partially within said chamberand including an output coupling loop extending through one of said endplates, said envelope also including a dome of material transparent toelectromagnetic waves sealed across said one end plate, said domeprojecting into said load member whereby said loop provides a directmagnetic coupling between said circuit and load member.

12. Electronic tube apparatus for supplying high frequency oscillationsto a hollow, conductive load member comprising a vacuum-tight envelopehaving therein a chamber, a magnet coil immediately surrounding saidchamber and having an external shell of magnetic material, said chamberincluding a pair of end plates of magnetic material connected with saidshell to provide a substantially complete enclosure of magnetic materialabout said coil and chamber,

whereby a field may be produced within said chamber between said plates,and a resonant circuit partially within said chamber and including anoutput coupling loop extending through one of said end plates, said loopconsisting of at least two sections both terminating substantially atthe center of said last-named end plate and each consisting of asub-loop extending from a region in said last-named end plate, displacedfrom said center, to said center, said envelope also in- 5 eluding adome of material transparent to electromagnetic waves sealed across saidone end plate and surrounding said output 100p, said dome being adaptedto project into said hollow load member whereby said loop providesdirect 5 magnetic coupling between said circuit and lead member.

13. Electronic tube apparatus for supplying high frequency oscillationsto a hollow, conductive load member comprising a vacuum-tight envelopehaving therein a chamber, a magnet coil vide a substantially completeenclosure of magnetic material about said coil and chamber, whereby afield may be produced within said chamber between said plates, and aresonant circuit partially within said chamber and including an outputcoupling loop extending through one of said end plates, said loopconsisting of at least two sub-loops, said envelope also including adome of material transparent to electromagnetic waves sealed across saidone end plate and surrounding said output loop, said dome being adaptedto project into said hollow load member whereby said loop providesdirect magnetic coupling between said circuit and load member.

14. Electronic tube apparatus for supplying high frequency oscillationsto a hollow, conductive load member comprising a vacuum-tight envelopehaving therein a chamber, a magnet coil immediately surrounding saidchamber and having an external shell of magnetic material, said chamberincluding a pair of end plates of magnetic material connected withsaidshell to provide a substantially complete enclosure ofma neticmaterial about said coil and chamber, whereby a field may be producedwithin said chamber between said plates, and a resonant circuitpartially within said chamber and including an output coupling loopextending through one of said end plates, said loopconsisting' of atleast two sub loops connected together at a region in said last-namedend plate, said envelope also including a dome of material transparentto electromagnetic waves sealed across said one end plate andsurrounding said output loop, said dome being adapted to project intosaid hollow load member whereby said loop provides direct magneticcoupling between said circuit and load member.

15. Electronic tube apparatus for supplying high frequency oscillationsto a hollow, conductive load member comprising a vacuum-tight ens velopehaving therein a chamber, a magnet coil immediately surrounding saidchamber and having an external shell of magnetic material, said chamberincluding a pair of end plates of magnetic material connected with saidshell to provide a substantially complete enclosure of magnetic materialabout said coil and chamber, whereby a field may be produced within saidchamber between said plates, and a resonant circuit partially withinsaid chamber and including an output coupling loop extending through oneof said end plates, and means connected'to said loop to reduce theinfluence of the inductance of said loops on said resonant circuit; saidenvelope also including a dome of material transparent toelectromagnetic waves sealed across said one end plate and surroundingsaid output loop, said dome being adapted to project into said hollowload member wherebysaid loop provides direct magnetic coupling betweensaid circuit and load member.

16. Electronic tube apparatus for supplying high frequency oscillationsto azhollow, conductive load member comprising a vacuum-tight envelopehaving therein a chamber, a" magnet coil immediately surrounding saidchamber and having an external shell of magnetic material, said chamberincluding a pair of end plates of magnetic material connected with saidshell to provide a substantially complete enclosure of magnetic materialabout said coil and chamber, whereby a field may be produced within saidchamber between said plates, and a resonant circuit partially withinsaid chamber and including an output coupling loop extending through oneof said end plates, and a metal shield connected across the outer endsof said'loop to reduce the influence of the inductance of said loops onsaid resonant circuit, said envelope also including a dome of materialtransparent to electromagnetic waves sealed across said one end plateand surrounding said output loop, said dome being adapted toproject'into said hollow 12 load member whereby said loop providesdirect magnetic coupling between said circuit and load member.

17. Electronic tube apparatus for supplying high frequency oscillationsto a hollow, conductiveloadmember comprising a vacuum-tight envelopehaving therein a chamber, a magnet coil immediately surrounding saidchamber and having' an external shell of magnetic material, said chamberincluding a pair of end plates of magnetic material connected with saidshell to provide a substantially complete enclosure of magnetic materialabout saidcoil and chamber, whereby a field may be produced within saidchamber between said plates, and a resonant circuit partially withinsaid chamber and including an output coupling. loop extending throughone of said end plates, said resonant circuitine eluding an anode memberand the terminals of said loop being connected to said anode mem-- bers,saidenvelope also including a dome of ma-. terial transparent toelectromagnetic waves sealed. across said one end plate and surrounding:said: output loop, said dome being adapted to'project into'said hollowload'member whereby said loop provides direct magneticv coupling betweensaid'lcircuit and load member;

18. In combination, a vacuum-tight envelope forminga chamber, a magnetcoil immediately surrounding, said: chamber and having an externalshellof magnetic material, said chamber including a pair of end platesof magnetic material connected with saidshell to provide a substantiallycomplete enclosure of magnetic material about said coil and chamber,whereby a field may be produced-within said chamber between said plates,and a resonant circuit partially within said-chamber and including anoutput coupling loop extending through one of said end plates, saidenvelope also including a dome of material transparent toelectromagnetic waves sealed'across said one endplate and surrounding:said-output-loop, saiddome being adapted to-project into a hollow loadmember whereby said loopprovides direct-magnetic coupling-between saidcircuit and load member.

DAVID H. SLOAN.

REFERENCES CITED The following references. are of record in the file ofthis patent:.

UNITED STATES PATENTS Number Name Date 841,386 De Forest Jan. 15, 1907'2,103,303 Steenbeck Dec. 28, 1937 2,305,884 Litton Q. Dec. 22, 19422,352,657" Potts July 4, 1944 2,391,016 Ginzton et a1 Dec.'l8', 19452,406,277 Bondley Aug.'20, 1946 2,414,085 Hartman Jan. 14, 19472,424,886 l-lan'scll July 29, 1947- 2,43l,94l Kihn Dec. 2, 19472,433,074 Tuller Dec. 23, 1947 FOREIGN PATENTS Number Country Date443,077 Great Britain Feb. 20, 1936

